PROJECT SUMMARY ABSTRACT HIV infection results in CNS complications, with nearly 75% of patients with advanced HIV disease showing neurological manifestations. Additional sequelae have patients on long-term successful cART therapy who suffer from residual and end organ diseases of HIV infection. Endothelial and glial cell dysfunction are central to HIV neuropathogenesis. A compromised neurovascular unit (NVU) results in increased leukocyte transmigration, HIV infection, and the establishment of a highly inflammatory environment, which further aggravates HIV-associated neurological disease. Extracellular vesicles are secreted from nearly every cell type, including glia. Many types exist, which we shall refer to collectively as EVs. They are released into the circulation, influencing intercellular communication at both local and distant sites from their cellular source. Thus, barrier endothelial cells, and the underlying neurons and glia (collectively referred to as the neurovascular unit) are constantly exposed to EVs. Infection with SIV or HIV can affect the composition of EVs, facilitating viral pathogenesis and spread. EVs from productively-infected cells in the periphery can contain viral proteins, host microRNAs and proteins that trigger responses in the neurovascular unit, all of which can promote S/HIV neuropathogenesis. Our collaborators showed this for EVs circulating in HIV-associated cancer patients and animal models (1). It is reasonable to assume that EVs containing viral proteins, especially Nef, could contribute to HIV-associated neurological complications. Several studies have demonstrated that these proteins independently trigger distinct changes in glial cell function through activation of Toll-like receptors. However, EV production, composition and function, especially in the context of SIV infection, represents a significant gap in our knowledge. Therefore, there is a critical need to understand the role of EVs in SIV neuropathogenesis and how the cell of origin influences SIV EV-induced intercellular communication. This R21 application seeks to address how the cell of origin influences EV cargo and how EV from SIV-infected cells affect blood-brain barrier permeability, endothelial and glial cell dysfunction.